Control system



Dec; '17, 1946. v

K. K. BOWMAN ETAL 2,412,864

CONTROL sYsTEy 2 Shets-Sheet 1 Original Filed Aug. 20, 1937 I as 3 Figl.

- a "Q Q s g A g III. "I I?) I v v n I! I N 2 g N N g b l L Inventors: N

Garold A. Kane Kenneth K. Bowman,

' The ttorney Dec. 17, 1946. K.'K. BOWMAN ETAL 2,412,864

CONTROL SYSTEM Original Filed Aug. 20, 1937 2 Sheets-Sheet 2 5 g 2 Mr 33 Y s Q I\ $2 I g rd w 3 .9 r;

5- 3* n .1 J m Inventors Garold A. Kane, Kenneth KB man,

M Thei Attorney.

' Patented Dec. 11, 1946 CONTROL SYSTEM Kenneth K. Bowman and Garold'A.Kane, Scotia,

N. Y., assignors to General Electric Company, a corporation of New YorkApplication August 26*, 1937, SerialNo. 160,092

Ren wed June 13, 1939 This inventlon relates tocontrol systems, moreparticularly to follow-up control systems and the 19 Claims. (01.172-239) like, in which a driven object is caused to move intopositional agreement with a. pilot device so as to reproduce themovements and positions of the pilot device, and an object oftheinvention is the provision of a simple, reliable, improved andinexpensive device'of this character.

Heretofore, follow-up systems have been utilized in which electricvalves have been employed for controlling the driving means of thesystem. These systems have given satisfactory and accurate operation.However, electric valves are expensive, have a definite lite andtherefore require replacement at intervals. Furthermore, the circuitsare often very complicated and not well understood by operators andattendants, and repairs and maintenance are therefore diflicult.Accordingly, a, more specific object of the invention is the provisionof a followup system that possesses substantially the same degree ofaccuracy as a follow-up system utilizing electric valves but one that isconsiderably less expensive, and so simple in construction, circuitarrangement and operation as to be readily comprehended by operators andattendants.

Follow-up systems are subject to the disadvantage of oscillation orhunting of the driven object about the position of correspondence withthe pilot device unless special means are provided to eliminate thisdifficulty. Electric transmitting and receiving devices are frequentlyemployed in follow-up systems for esponding to positional disagreementof the pi ot device'tand driven object to control the driving means.

A further object of this invention is the provision of entirelyelectrical means for introducing an anti-hunting correction into thewindings of the electrical motion receiving device so that no torque isimposed mechanically on the receiving an operating condition of thedriving means are provided for introducing a correction so assubstantially to eliminate hunting. In a specific 2 embodiment, theanti-hunting means are responsive to the torque oi. the driving meansand the correction is introduced so as to control the bridge toanticipate the position of correspondence and.

to reduce the driving torque so as substantially to eliminate hunting. 7

In illustrating the invention in one form thereof, it is shown asembodied in a follow up sys-.

tem for causing a Searchlight to move into positional agreement with asighting device. It will be understood, however, thatthe invention hasother applications.

For a better and more complete understanding of the invention referenceshould now be had to the following specification and to the accom--panying drawings in which Fig. 1 is a simple diagrammaticrepresentation-of an embodiment of the invention; Fig. 2 is a chart ofoperating characteristics; andFig. 3 is a simple diagram matic sketch ofa modification.

to the drive shaft of which the Searchlight is.

connected by means of gearing i8 and it. As shown, motor I! is of thedirect current type and is supplied with powerirom a suitable sourcerepresented in the drawings by the supply lines ii. The supply ofcurrent to motor i2 is controlled by suitable means illustrated as aWheatstone bridge it. As indicated in the drawings, the upper side ofthe bridge It comprises resistance arms I8. and its and the lower sideof the bridge comprises resistance arms I and lie. diagonally oppositepoints I1 and I8 01 the bridge are connected to opposite sides or thesource I! and the remaining diagonally opposite bridge points I! and 20are connected to the armature terminals of the motor l2. Bridge point I!is connected to one armature terminal oi. the motor l2 by means ofconductors 2| and 22 and the diagonally opposite bridge point 20 isconnected through resistance 28 and conductor 24 to the oppositeterminal of the motor armature.

Motor i2 is provided with a direct current field winding I!- which issupplied from a suitable source such as the source I5 to which it isconnected by means of conductors 25, 28 and 21.

When the bridge i6 is balanced, the'voltages of the diagonally oppositebridge points I! and 20 are equal and no current is supplied to themotor I! and the latter is therefore at standstill.

Searchlight i0 is driven'by The ' for actuating the rocker arm 28.

' sponsive to positional disagreement of the pilot.

device II and the driven object III are provided These means areillustrated as high and low speed self-synchronous electrical motiontransmission systems 29 and 30, respectively. The high speed motiontransmission system comprises an electrical motion transmitting device31 and an electricalmotion receiving device 32, and similarly the lowspeed electrical motion transmission system comprises a transmittingdevice 33 and a receiving device 34. The rotor member of the transmitter3i is connected to the telescope ll through a suitable gear train so asto rotate at a suitable high speed ratio such as 36 to 1 with therotation of the telescope, while the rotor of the transmitting device 33is preferably driven in a 1 to 1 ratio with the telescope. Thus, foreach'degree of rotation of the telescope Ii, the rotor of the high speedtransmitting device 3| rotates 36 and consequently a very fine andaccurate control is obtained.

The transmitting and receiving instruments 3| to 34 inclusive'may be ofany suitable type. Preferably an alternating current type is employed,each instrument being provided with a polycircuit armature winding andwith a field winding. -As-shown, the transmitters 3| and 33 are providedwith flield windings 3h. and 33; re.

. spectively on their rotor members and with delta connected, bi-poiar,three-phase armature windings 3 lb and 33h respectively on their tatormembers. The receiver 34 is similar in construction to the transmitters3| and, 33. Corresponding points of the armature windings of thereceiver 34 and the transmitter 33 are connected together by means ofthree conductors 35 and similarly corresponding points of the armaturewindings v of thereceiver 32 and transmitter 31 are connected togetherby means of the three conductors 36. The single phase field windings oftransmitters 3| and 33 and receiver 34 are supplied with alternatingcurrent from a suitable source such as that represented by the supplylines 31 to which these windings are connected by means of conductors38.

The 'rotor member of the high speed receiving device 32 differs from therotor memberof the low speed receiving device 34 in that it is providedwith a polycircuit distributed winding 32a. This winding is shown as adelta connected winding and one of the delta points is connected bymeans of conductor 33 to one side of the alternating current source 31.The other two delta points of this winding are connected by mean of oductors 40 and 4| to the terminals of the secondary winding of. atransformer 42, the mid-- point of which winding is connected by meansof conductor 43 to the other side or the alternating current source 31.

The arms I6, lib, Hie and l6a oi the bridge are preferably resistors andeach of these arms is provided with a plurality 'oftaps as shown. Eachtap in turn is provided with a flexible contact. preferably a resilientheat-tempered spring contact. Thespring contacts for the two arms l6.and lBb comprising the upper side or the bridge are arranged inv a rowHe, and similarly the spring contacts for the arms I Be and Isa,constituting the lower side of the bridge, are arranged in a row l6:spaced from the upper. row. Each contact is initially adjusted so thatit is are undeflected. When the contact rocker arm 28 is in the centralor null position in which itis shown, all of the spring contacts are intheir undeflected positions and the bridge is balanced so that novoltage issupplied to the motor l2. It the rocker arm 23 is rotated in acounterclockwise direction it engages the first spring contact for thearm I6; and also the first spring contact for the arm ltd. As therotation of the arm 28 continues the first contacts of arm 16-. andi6dare deflected into engagement with the second contacts of the armsI6. and lie thereby short circuiting a portion or the resistance of eachof the arms lBa and 16a. If the rotation of the arm 28 is continued toits extreme left-hand position, the second contacts of each or the armswill be forced into engagement with the third contacts, 'etc., and thusthe individual portions of the resistance arms 16. and IE4 aresuccessively short circuited untilthe entire arms are short circuited.This of course produces maximum unbalance of the brid e and maximumvoltage is supplied to the armature of motor I2. Similarly, clockwiserotation of the contact rocker arm 28 from its central and lowerposition produces successive short circuiting of the opposite bridgearms [6s and |6c until in the extreme right-hand .of reverse polarity issupplied to the motor l2 so as to cause it to rotate in the reversedirection.

Resistors 52d and 52 are connected across movable contact 52:. andstationary contacts 52:; and 52 respectively so that a definite amountof current always flows from source 52: through the operating coils ofelectromagnets' 50 and SI.

In the central position in which armature A! is illustrated, it isunaffected by electromagnets -50 and 51. However, when the armatureisdisplaced from its zero position toward one of the electromagnets, thepull of the two electromagnets on the armature will be unequal. The pullof the electromagnet which the armature is approaching will increase andthe pull of the other will decrease. This increasing pull builds up in aparabolic relationship with respect to the distance between magnet.

the armature and the electro- This featurehas several importantadvantage The error in a system of this character is a function of themovement of the rocker arm 23 and the pressure which it exerts againstthe spring contacts [6e and IE1. Hence, reducing this pressure increasesthe accuracy of the system or permits the use of heavier springcontacts, or a greater number thereof for the same accuracy.

The use of heavier spring contacts increases the maximum possible poweroutput of theequipment.

Another advantage is the reduction of interference between units.Assume, for example, that four units are connected to one director ortransmitting unit and that a fifth unit is to be connected andsynchronized with the other units and the director. In this example, thedirector conauaseo able power is required to prevent it from rotatingtoo fast. This power must-come from the high speed receiving device, andthis device in turn reacts through the electrical connections on theother four high speed receiving devices, to cause them to oscillatethrough a small arc. By utilizingthe spring contact pressurecompensating means, the output of the heart'cain can be made lowerthanotherwise would be necessary and the reaction of the high speedreceiving devices on each other can be reduced to such an extent as tobecome unobjectionable.

The rotor member of the high speed receiving device 32 is connected tothe contact rocker arm 28 through a yieldable coupling comprising aheart-shaped cam 44 with which cooperates a springpressed roller 45. Asshown, the cam 44 is mounted on the rotor shaft of receiving device 32and the roller 45 is carried on the end of an arm 45 which is pivotallymounted on a frame 41. Bearing against the arm 46 is a helical spring 48which forces the arm towards the .heart cam and thereby maintains theroller in engagement with the cam. The heart cam'is constructedandarranged on its shaft in such a manner that the roller 45 is caused by.the spring to seek a position of rest at the base of the cam, as shownin the drawings. The frame 41 is directly connected tothe rocker arm 28as indicated.

Thus it will be seen that a limited rotation of the cam 44 in eitherdirection from the central or position in which it is shown will effecta rotation of the rocker arm 28 in a corresponding direction. However,if the rocker arm 28 is actuated to an extreme position the cam 44 cancontinue its rotation while the rocker arm 28 remains stationary in itsextreme position.

The contact rocker arm 28 is provided with an armature member 49arranged between two solenoids 50 and 5|. A A selector switch 52 havinga movable contact member 52a and two stationary 7 contacts 52b and 52ais provided for selectively energizing the solenoids 5| and 50. Themovable contact ih is connected to the rotor of the low speed receivingdevice 34 through the yielding connection comprising the heart-cam 53,spring pressed roller 54 and carrying frame 55 which is identical withthe heart-cam 44 and its cooperating mechanism described in theforegoing. As shown, the stator members of the receiving devices 32 and34 are rotatably mounted and geared to the shaft of the drive motor 12and hence are connected to the driven object Hi. The ratio of thegearing between the motor l2 and the statormember of the high speedreceiving device 321s the same as that between the telescope H and therotor of the transmitting. device 3!, which in this particular case isassumed to be 36 to 1. Similarly, the ratio of the gearing between thestator member of the receiving device 34 and the motor 12 is the same asthe ratio of the gearing between the telescope H and the rotor member ofthe transmitter 33 which was assumed'to be 1 to 1.

As is well understood, electrical motion transmitting and receivindevices connected and energized in the manner described for theinstruments ",22, II and 44, have the property of self-synchronism. Inother words. if the stator member of the receiving device 32 isrestrained nd the rotor member of the transmitting device 3| is turnedfrom the original position with respect to its stator winding in whichit is shown I to a new position, the rotor member of the receivingdevice will turn to a corresponding position with respect to its statorwinding. Thus, if the-rotor member of the transmitter Si is rotated agiven angle, e. g., 10 in a clockwise direction and the stator member ofthe receiving device 32 is restrained, the rotor member of the receiverwill rotate 10 in a clockwise direction and the rotor members of bothdevices will again be in positions of correspondence with respect totheir stator windings. It will also be noted that if the rotor member ofreceiver 32 remains at rest and the stator member is rotated 10 in acounterclockwise direction while the rotor member of thetransmittingdevice 3| is'beihg rotated 10 in a clockwise direction therotor.

member of the receiver would be in the same position with respect to itsstator winding as if it had rotated in a clockwise direction and thestator member had remained at rest. In

other words, if the stator member of the receiving device is rotated ina direction opposite to that in which the rotor member tends to rotateand at the same speed as that at which the rotor of the transmitterrotates, the rotor member of the receiver will remain standing still inspace. Thisis also true of the transmitting and receiving devices 33 and34. When the driven ob-# ject i0 is in correspondence, i. e., inpositional agreement with the pilot device II, the rotors and stators ofthe transmitting and receiving devices ii to 34, inclusive, are in thepositions in which they are illustrated in the drawings.

In order to prevent hunting, an anti-hunting device is provided,comprising two saturable core reactors 58 and 51. The alternatingcurrent windings 58a and 51. respectively, of these reactors areconnectedin parallel to form a bridge as shown, and are supplied from asuitable source of alternating voltage represented by the supply lines58. Source 58 may be, and preferably is, the same source as thatrepresented by supply lines 31. Reactors 55 and 57 are provided withdirect current magnetization control windings 59 and 60. These twowindings are connected in series relationship as indicated and aresupplied with direcct current from a suitable source such as thatrepresented by the supply lines I5 to which they are connected throughthe resistor t. The reactors 56. and 51 are also provided with directcurrent windings 62 and 63. These direct current windings 62 and 63 areconnected in parallel relationship with each other across a portion ofthe resistor 23 so that they are energized in accordance with thecurrent supplied to the driving motor l2.

When the direct current magnetization of a that with the motor currentin one direction the coil 62 aids the coil 59 and the coil 63 bucks thecoil 60. The primary winding, of the transformer 42 is connected acrossthe diagonally opposite points of the bridge formed by the twoalternating current coils 56a and 51a. When no current is flowing in thearmature circuit of the motor I2, and consequently no current is flowingin the coils B2 and 53, the bridge is balanced and no voltage is appliedto the primary winding of the transformer 42. If current is'flowing inthe motor circuit the bridge is unbalanced in; one direction or theother and a voltage is applied to the primary winding of the transformer42, and this voltage is supplied through the transformer 42 to the rotorwinding of the receiving device 32 in such a direction that a torque isproduced which causes the rotor mem-' ber of the receiver 32 to turn insuch a direction as to rotate the rocker arm 23 in a direction to reducethe current supplied to the motor l2,

As shown in the drawings, reactors 56 and 51 are also provided withshort circuited stabi- '53 whereas the magnetization of the coil S'Lwillaid the magnetization of the coil 30. These two coils 66 and 61 areconnected across a portion of the resistor 68 which is connected acrossthe brushes of the motor I2 through the resistor 23. Thus the coils 66and 51 are energized in accordance with the counter-voltage oi the motorand therefore in accordance with its speed.

With the foregoing understanding of the elements and their arrangementand connection in the system, the operation of the system itself will bereadily understood from the following detailed description.

Assuming the system to be at rest and assuming the driven object to bein positional agreement with the pilot device, the apparatus is in thecondition in which it is illustrated in the drawings. The directorhandle (not shown) is turned to rotate the telescope II. This producesrotation of the rotors of the transmitters 3| and 33. The rotor of thetransmitter 3| rotates 36 for each degree of rotation of the telescopeand the rotor of the transmitter 33 which rotates at the same speed asthe telescope. Since the motor l2 and the searchlight iii are at restwhen the telescope l I is first moved, the stator members of thereceivers 32 and 34 are restrained against movement and consequently therotors of the receivers rotate in correspondence with the rotors oftheir respective transmitting devices. Assuming clockwise rotation ofthe rotor members of the transmitting devices, the rotors of thereceiving devices will also rotate in a clockwise direction. Clockwiserotation of the rotor of the receiver 32 will produce clockwise rotationof the cam 44 and also. clockwise rotation of the contact rocker arm 28,and as previously explained, clockwise rotation of the rocker arm 23will sue-- cessively short circuit portions or the arms lit and lie ofthe bridge l6 and thus produce an unbalance of the bridge so that :avoltage is supplied to the armature of motor l2. This voltage causes themotor 12 to rotate in a direction to drive the sealchlight in intocorrespondence with the telescope II. The gearing between the motorwhich the rotors are rotated. The motor l2 ac-.

celerates rapidly and when its speed has increased to the value at whichthe stator member of the receiver 32 is driven counterclockwise at thesame speed as the speed at which the rotor member of the transmitter isrotating in a clockwise direction the rotor member of the receiver 32will come to rest in space. At this point the rotor member of thereceiver is rotated from its initial position by an amount necessary todeflect the rocker arm to a position to produce an unbalance of thebridge and a voltage sufllcient to cause the motor l2 to drive thesearchlight ill at a speed equal to the speed at which the telescope His rotating. 1 The rotor member of re-,- ceiver 34 is rotated aproportional amount, 1. e., one thirty-sixth of the rotation of receiver32. If the speed of the director is further increased, the rotor membersof the receivers 32 and 34 will rotate in a clockwise direction therebycausing more of the flexible contacts to be short circuited by therocker arm 28 and the speed of 7 themotor l2 and the Searchlight l0correspondthe transmitter 33 having been assumed).

ingly increased. When the speed of the searchlight it) becomes equal tothat of the telescope H the stator members of the receivers 32-and 34will be driven in a counterclockwise direction at the same speed as therotors of the transmitters 3| and 33 are being driven in a clockwisedirection and consequently the rotors of the receivers 32 and 34 willagain come to rest.

If the speed of the telescope H is increased to the maximum speed atwhich the motor l2 can drive the Searchlight Hi, the rocker arm 28 willbe in its extreme right-hand osition in which all of the portions of thebridge arms I61 and 6c are short circuited and the rotors of thereceivers 32 and 34 will again come to rest. The rotor'member ofreceiver 32 will be rotated from its initial position Just sufiicientlyto cause {the rocker-arm 28 to be maintained in its extreme right-handposition. This will produce maximum unbalance of the bridge and maximumpower will be supplied to the motor l2 causing it to rotate thesearchlighl; l 0 at maximum speed. Under these conditions the armature49 attached to the rocker arm 28 will be in proximity or in engagementwith the core oi the solenoid 50. However, if the speed of the telescopel I is further increased the rotors of the receiving devices 32 and 34would begin to rotate, and since the speed of the motor l2 cannot befurther increased the rotors of the receivers would continue to rotateas long as the telescope H is rotated at this increased speed. Theheartcams 44 and 53 permit this continuous rotation. As soon as heart cam 53has rotated a small amount, depending upon the setting of the contact 52the movable contact member 52. would engage the stationary contactmember 52 (clockwise rotationv oi the rotor of This completes anenergizing circuit for the solenoid 50, which in response toenergization attracts and holds the armature 43 so that the contactrocker arm 28 is held in the maximum power position irrespective of theheart cam 44 which is kept in rotation by the rotation of the rotor ofthe 'receiver 32 as long as the speed of the telescope is greater thanthe maximum speed at which the motor 12 can drive the searchlight Hi.The amount of rotation of the rotor of receiver 34 and cam 53 necessaryto cause movable contact 2% of their initial positions.

member 82 to engage either of its cooperating stationary contacts may beany desired amount,

for example 2 5". Since the speed ratiobetween the rotors of receivers32 and 34 is 36:1 it will be noted that 2 /2 movement of the rotor ofreceiver 34 and cam 53 qfrom their initial position corresponds to 90rotation of the rotor of receiver 82 and cam 44 from their initialposition.

Now it the telescope H is suddenly decelerated and stopped the movablecontact member 52- will remain in engagement with stationary contactmember 820 until motor l2 has driven searchlight "I to within 2 ofcorrespondence with the telescope or in other words until the rotor ofreceiver 84- and the cam 58 approach to within At this point the rotorof high speed receiver 32 and cam 44 will be within 90 of their initialpositions. As the movable member 52. breaks contact with the stationarymember 52 the contact rocker arm 28 will still be rotated from itsoriginal position by the heart cam 44 until the stator member of highspeed receiver 82 is driven by motor l2 an amount suflicient to rotatethe rotor member of receiver 32 and the cam 44 to their initialpositions and at this point the searchlight l0 will be in correspondencewith the telescope H. As thus far described power would be kept on themotor I: until the instant that the searchlight l0 reachedcorrespondence withthe telescope ll. I1 this were the case, the storedenergy of the motor l2 and the searchlight l0 would cause thesearchlight In to overshoot the position of correspondence and thecontrol would then be actuated in the reverse direction to return thesearchlight r in the opposite. direction to a position of correspondenceagain with the telescope. But again power would be kept on the motor l2until the searchlight reached correspondence with the telescope and thiswould cause the Searchlight to overshoot in the reverse direction. As aresult continuous oscillation or hunting would be set up and theSearchlight would not come to rest in correspondence to the telescope.

However, this continuous oscillation or hunting is prevented by theanti-hunting means 55, 51.

The manner in which the anti-hunting means functions substantially toeliminate hunting will best be understood by referring to the chart ofcharacteristic curves in Fig. 2. As shown in Fig.

2, curve 69 represents the relationship between displacement of therocker arm 28 from its central or zero position and the error orpositional disagreement between the searchlight I0 and telescope. II,with the rotor of the motor I2 blocked so as to prevent it from rotatingand with the anti-hunting means 56, 51 disconnected or otherwiserendered inactive. This relationship is seen to be substantially a.straight-line relationship. With the rotor of the motor blocked, thecurrent supplied to the motor is proportional to the displacement of therocker arm 28 and consequently curve 88 also represents the relationshipbetween motor current and error. Curve 10 represents the samerelationship between displacement of the rocker arm or motor current andthe error but with the anti-hunting means 58, 51 connected andfunctioning. Thus it will be noted that for any value 01' error theanti-hunting means functions to rotate the contact rocker arm 28 in adirectionto reduce the current supplied to the motor because the flow ofmotor current acts through the anti-hunting means to impose adisplacement of the contact rocker arm toward zero. The response betweenAs a simple illustrationot the stabilizing action of the anti-huntingcircuit. let it be assumed that the director has been brought tostandstill, and that the Searchlight is synchronizing, i, e., cominginto correspondence with the telescope. Eventually, the error becomesreduced to zero, but on account or the stored energy, the searchlightwill overshoot and'the .error will increase in a negative direction.When theerror becomes negative, the contact rocker arm 28 follows theerror very closely and motor current is estab-' lished to decelerate andreverse the motor. This current gives rise to the delayed anti-huntingsignal so that as the error increases in the negative direction, thecontact arm proceeds along the dotted curve to some point such as a atwhich point the 'searchlight is at standstill and the rate of change oferror is zero. The gradual departure of the'dotted curve from the curve89 toward the curve 18 as the error increases is caused by the gradualbuilding up of the anti-hunting signal. When the error becomes maximumand begins to decrease, the position oi. the contact arm will be asshown by the continuationof the dotted line from the point a to thepoint 8 atwhich point the erroris again zero. This position of the curvelies closer to the zero ordinate axis than does the curve III on accountof the fact that the decreasing value of the anti-hunting eifect isdelayed. Now, when the error first passed through zero, the speed of thesearchlight was relatively high and represented a considerable I amountof stored energy. As the error increased negatively, the torque tendingto reduce the speed of the Searchlight was high as shown by the dottedcurve up to the point a at which point there exists no stored energybecause the search light is momentarily at standstill. .Now, as the'searchlight is driven back toward the position of zero error, thedriving torque is relatively low as shown by the dotted curve fromthepointa to the point 0 so that at point 0 the stored energy is much lessthan when the error first became zero. Now if the searchlight carries onthrough zero the over-travel will be very small and will reach only to apoint D on curve 10,- a much smaller overtravel than represented by thepoint a. As the error again decreases from the point D to the point 0,zero error and zero speed will probably occur simultaneously and nofurther overshooting occur. Thus it will be seen that the anti-huntingsystem effectually prevents any sustained or cumulative hunting actionand promptly brings the driven object I0 into correspondence or tostandstill in correspondence with the pilot device.

The error correction means, i. e.. the coils 68 and 61, operate in verymuch the same manner as the anti-hunting device. As previously pointedout, these coils are energized by the counter voltage of the motor I2which is directly proportional to the speed of the motor. This voltageis applied to the coils 68 and 61 in such a manner as to vary thebalance of the reactor bridge so that a voltage is supplied to thereceiver 32 which produces a torque tending to rotate the Co tact rockerarm 28 in a" direction to reduce to introduce supporting member ageacross resistor 11 the correspondence error between the driven objectill and the pilot device ii.

In the modification of Fig. '3 the pilot device 1|, driven object 12,Wheatstone bridge 18, antihunting means 1|, driving motor 15, high andlow speed cams 16 and 11, and selective switch 18 are substantiallyidentical in structure and function with corresponding elements in thesystem of Fig. 1. The arrangement of Fig. 3 differs from the system ofFig. 1 primarily in that the electrical motion transmitting andreceiving system of Fig. 1 is replaced by a mechanical differentialdevice 19 for actuating the high and low speed cam mechanism 18 and 11.The arrangement of Fig. 3 also differs from the arrangement of Fig. 1 inthat a flexible connection 80 is included in the connections between thehigh speed cam. mechanism 16 and the contact rocker arm 8| and furtherdiffers from the arrangement of Fig. 1 in the connection of thealternating current coils 82 and 88 of the anti-hunting mechanism forcontrolling the flexible connection 80 the anti-hunting and speedcorrection.

A mechanical differential member 19 has an input gear 19. which isconnected throughgearings 84, 85 and 86 to the pilot device 1|. Also thedifferential device has a second input gear 19s that is connectedthrough the gearing 81 to the drive shaft of the motor 15 which drivesthe driven object 12. The output member of the differential 18 comprisesa cage member 19 carrying gears 'I9aand 18 which mesh with the gears 19.and19n. The cage member 19 is mechanically connected to the output shaft88 which passes through the hub of the upper gear 81 and is connected tothe high speed heart cam 15. As shown, the output shaft 88 is alsoconnected through gearing 89 and 98 to a low speed cam 11.

Flexible connection 80 comprises a T-shaped supporting member 88. whichis secured to the shaft of the frame member 16. which carries the roller18s that engages the high speed cam 18. The support 80. is provided withelectromagnets 9| and 92 and a flexible member 93 rigidly mounted on thesupport 88. and arranged to extend between the cores of theelectromagnets 9i and 92. The input shaft 94 of the contact rocker arm8| is provided with a crank arm 95 connected slidably with the spring 98so as to rotate the shaft 94 in response to pivotal movement of the 88..Spring 93 is so still that it does not bend in normal operation of thecontacts. The operating coil of electromagnet 9| is connected from theupper side of the supply source 95 through the lower reactor coil 89 tothe opposite side of the supply source whereas the operating coil ofelectromagnet 92 is connected through the upper reactor coil 82 to theopposite side of the supply source; When a large current flows in thearmature circuit of motor 15 the volt- 91 causes the impedance of one ofthe reactor coils 82 or 88 to increase and the other to decrease. Thiscauses the current flowing through one of the electromagnets 8| and 92to incraese and the current flowing through the other to decrease. Hencethe spring 98 is deflected thus shifting the contact rocker arm 8| aproportional amount. Thus the antihunting device 14 functions in amanner similar to that of the anti-hunting device 56, 51 of Fig. 1 butthe anti-hunting correction is introduced into the connections betweenthe high speed cam and the contact rocker arm by means of electromagnets9| and 92 and flexible connection 88 instead of being introduced intothe rotor winding of an electrical motion receiving device as in thesystem of Fig. 1.

In operation, rotation of the telescope 1| with the motor 15 at restproduces rotation of the output shaft 88 of the difierential device andthis rotation is transmitted through the high speed cam 18 and flexibleconnections 88 to the contact rocker arm 8| which rotates to unbalancethe bridge and energize the motor 15 for rotation in a direction todrive the driven object 12 toward correspondence with telescope. Asmotor 15 rotates it revolves the input member 19:; of the differentialtending to return the contact arm 8| to its original position.

The anti-hunting operation is the same as in the system of Fig. 1 exceptas to the differences explained in the foregoing.

' The'self-synchronous and error correction features are accomplished inexactly the same manner as previously described for the arrangement ofFig. 1.

Although in accordance with the provisions of the patent statutes thisinvention is described as embodied in concrete form it will beunderstood that the apparatus and elements shown are merely illustrativeand that the invention is not limited thereto since alterations andmodifications will readily suggest themselves to persons skilled in theart without departing from the true spirit of the invention or from thescope of the annexed claims.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

l. A follow-up system for controlling a driven object to move inpositional agreement with a pilot device comprising an electric motorfor driving said object, a Wheatstone bridge having opposite bridgepoints connected to said motor each arm of said bridge having aplurality of taps each having a flexible contact, the contacts foropposite sides of said bridge being separated from each other andarranged in groups, a movable member for actuating said contacts, meansresponsive to positional disagreement of said pilot device and drivenobject for actuating said movable member to successively short-circuitportions of opposite arms of said bridge to effect unbalance thereof andenergization of said motor to drive said object toward correspondencewith said pilot device comprising a cam for actuating said movablemember, an electrical motion transmitting device connected to said pilotdevice, and an electrical motion receivin device electrically connectedto said transmitting device, said receiving device having a rotorelement and a rotatably mounted stator element, one of said elementsbeing mechanically connected to said cam and the other beingmechanically connected to said driven object and anti-hunting meanscomprising an electrical device having a stationary winding connmted tobe responsive to an electrical operating condition of said motor and asecond stationary winding controlled by said first winding and meansconnected to and controlled by said second stationary winding foractuating said movable meinber to substantially eliminate hunting.

2. A follow-up system for causing a driven ob- Ject to move intopositional correspondence with a pilot-device comprising in combinationan electric motor for driving said object, a Wheatstone bridge forcontrolling the energization of said motor, each arm of said bridgehaving a plurality of taps each provided with a flexible contact,thecontacts for opposite sides of said bridge being 13 rouped in rows, amovable member for actuating said contacts a cam for actuating saidmember, means responsive to positional disagreement of said pilot deviceand driven object for actuating said cam to cause said member tosuccessively short-circuit portions of opposite arms of said bridgethereby to unbalance said bridge and energize said motor to drive saidobject toward correspondence with said pilot device comprising anelectrical motion transmitting device connected to said pilot device, anelectrical motion receiving device having a rotor member connected tosaid cam and a rotatably mounted stator member provided with a windingconnected to the stator winding of said transmitting device andmechanically connected to said driven object and-antihunting meanscomprising a saturable reactor having a winding connected to thearmature circuit of said motor and a second winding controlled therebyand means connected to said second winding for actuating said-movablemember so as substantially to eliminate hunting.

3. A follow-up control system for causing a driven object to move intopositional agreement with a pilot device comprising an electric motorfor driving said object, a Wheatstone bridge for controlling theenergization of said motor, each arm of said bridge having a pluralityof taps each provided with a flexible contact, a movable member foractuating said contacts to unbalance said I bridge, means responsive topositional disagreedrive said object toward correspondence with saiddevice. at maximum.

4. A follow-up control system for causing a driven object to move intopositional agreement with a pilot device comprising an electric motorfor driving said object, a Wheatstone bridge for controlling theenergization of said motor, each arm of said bridge having a pluralityof taps each provided with a flexible contact, the contacts of oppositesides of said bridge bein grouped in respective rows, a movable memberfor actuating said contacts to short-circuit portions of opposite armsof said bridge to eiiect an unbalance, said member having a nullposition in which said bridge isbalanced and said motor is deenergized,and movable in one direction from said nullposition to a position inwhich portions of a pair of opposite bridge arms are short-clrcuitedandsaid motor is energized for rotation in one direction at maximum powerand movable in the op posite direction from said null position to aposition in which portions of the other pair of bridge arms areshort-circuited and said motor is energized for rotation in the oppositedirection at maximum power. said member being provided with an armature,a pair of electromagnets arranged in cooperative relationship therewith,means responsive to positional disagreement of said pilot device anddriven object for actuating said movable member in a direction toenergize said motor to drive said object toward correspondence with saiddevice, and means responsive to positional disagreement of said deviceand ob- Ject in excess of a predetermined amount for en-' ergizing oneof said electromagnets to attract said armature and hold said member inone of said maximum power positions.

5. A follow-up system for causing a driven object to move intopositional agreement with a pilot device comprising an electric motorfor driving said object, a Wheatstone bridge for controlling theenergization of said motor, the arms of said bridge having a pluralityof tapseach provided with a flexible contact, the contacts for oppositesides of said bridge being arranged in groups, a rotatable memberarranged between said groups for actuating said contacts toshort-circuit portions of opposite arms of said bridge, said memberhaving a null position in which said bridge is balanced and said motoris deenergized,

and two maximum power positions in which said motor is energized forrotation in opposite directions at maximum power, said rotatable memberbeing provided with an armature, a pair jof electromagnets arranged incooperative relationship with said armature, fine control meanscomprising an electrical motion transmitting system .eon nected tosaid-pilot device and driven obj'cfior operation at high speed withrespect thereto, and responsiveto a predetermined amount of positionaldisagreement of said device and object for actuating said member to oneof said maximum power positions, and coarse control means comprising asecond electrical motion transmitting system connected to said deviceand object for operation at relatively low speed with respect to saidhigh speed system and responsive to positional disagreement of saiddevice and object in excess of said predetermined amount for effectingenergization of one of said electromagnets to maintain said member insaid maximum power position) 6. A follow-up control system for causing adriven object to move into positional agreement with a pilot devicecomprising driving means for said object, means for controlling saiddriving means, means responsive to positional disagreewith said pilotdevice comprising an electrical motion transmitting device connected tosaid pilot device and an electrical motion receiving device electricallyconnected to said transmitting device and mechanically connected to saidobject, and anti-hunting means responsive to an operating condition ofsaid driving means .for supplying a current to said receiving device tocause said control means toreduce the torque of said driving means.

'7. A follow-up control system for causing a driven object to move intopositional agreement with a pilot device comprising in combination anelectric motor for driving said object, means for controlling thecurrent supplied to said motor, means responsive to positionaldisagreement of said pilot device and driven object for actuating saidcontrol means to cause said motor to drive said object towardcorrespondence with said pilot device comprising an electrical motiontransmitting device connected to said pilot device and an electricalmotion receiving device electrically con nected to said transmittingdevice and mechanically connected to said object, and anti-hunting meansfor substantially eliminating oscillation of said object about theposition of correspondence with said pilot device comprising anelectrical device having a winding connected to the armature circuit ofsaid motor to be responsive to an electrical operating condition of saidmotor and a second winding connected to said receiving device forsupplying current, to said receiving device to effect rotation thereofin a direction to reduce the current supplied to said motor. 4

-8. A follow-up control system for moving a driven object intopositional agreement with a pilot device comprising in combination anelectric motor for driving an object, means for controlling the supplyof current to said motor, means responsive to positional disagreement ofsaid pilot device and driven object for actuating said control means toenergize said motor to drive said object toward correspondence with saiddevice comprising an electrical motion transmitting device connected tosaid .pilot device and an electrical motion receiving device having tworelatively movablemembers each provided with a winding, one of saidmembers being mechanically connected to said object and one of saidwindings being connected to a corresponding winding of said transmittingdevice, and anti-hunting means responsive to the motor current forsupplying a current to one of said windings in a direction to actuatesaid control means to reduce the current supplied to said motor.

e 9. A follow-up control system 'for moving a driven object intopositional agreement with a pilot device comprising in combination anelectric motor for driving an object, means for controlling the supplyof current to said motor, means responsive to positional disagreement ofsaid pilot device and driven object for actuating said control means toenergize said motor to drive said object toward correspondence with saiddevice comprising an electrical motion transmitting device connected tosaid pilot device and an electrical motion receiving device having tworelatively movable members each provided with a winding, one of saidmembers being mechanically connected to said object and the othermechanically connected to said control means, one of said windings beingconnected to a corresponding winding of said transmitting device, andantihunting means responsive to the motor current for supplying acurrent to the other of said windings in a direction to cause saidreceiving device to actuate said control'means in a direction to reducethe motor current.

10. A follow-up control system for moving a driven object intopositional agreement with a pilot device comprising an electric motorfor driving said object, means for controlling the supply .of current tosaid motor, means responsive to pcsitional; disagreement of said deviceand object for actuating said control means to cause said motor to drivesaid object toward correspondence with said pilot device comprising, anelectrical motion transmitting device mechanically connected to-saidpilot device, an electrical motion receiving device having a rotormember and a rotatably mounted stator member, one of said members beingmechanically connected to said control means and the other of saidmembers being mechanically connected to said object, a winding on eachof said members, one of said windings being electrically connected to acorresponding winding of said transmitting device, and means responsiveto the current supplied to said motor for supplying a current to theother of said windings on said receiving device to affect rotation ofsaid receiving device in a direction to reduce the current to said motorthereby substantially to eliminate hunting. 1

11. A follow-up control system for causing a driven object to move intopositional agreement with a pilot device comprising in combination anelectric motor for driving said object, a Wheatstone bridge forcontrolling the supply of current to said motor, a movable member forcontrolling the balance of said bridge, means responsive to positionaldisagreement of said pilot device and driven object for actuating saidmember to unbalance said bridge thereby to supply current to said motorto cause said motor to drive said object toward correspondence with saiddevice at a speed dependent upon said disagreement, and saturablereactor means responsive to an electrical operating condition of saidmotor and means controlled by said reactor means for actuating saidmovable member in a direction to reduce the current to said motorthereby substantially to eliminate hunting.

12. A follow-up control system for moving a driven object intopositional agreement with a pilot device comprising in-cornbination, anelectric motor for driving said object, a Wheatstone bridge forcontrolling the supply of current to said motor, a movable member forcontrolling the balance of said bridge, means responsive to positionaldisagreement of said pilot device and driven object for actuating saidmember to unbalance said bridge and energize said motor to drive saidobject toward correspondence with said pilot device, a saturable corereactor having an alternating current winding, a direct current controlwinding on said reactor connected to be responsive to the motor currentfor controlling said al-' ternating current winding to produce avoltage, and means responsive to said voltage f or actuating saidmovable member to reduce the current to said motor thereby substantiallyto eliminate hunting.

13. A follow-up control system for causing a driven object to move intopositional agreement; with a pilot device comprising in combination, anelectric motor for driving said object, a Wheatstone bridge connected tosaid motor for controlling the supply of current to said motor, amovable member for controlling the balance of said bridge, meansresponsive to positional disagreement of said pilot device and drivenobject for actuating said movable member to unbalance said bridge tocause said motor to drive said object toward correspondence with saiddevice comprising an electrical motion transmitting device connected tosaid pilot device and an electrical motion receiving device electricallyconnected to said transmitting device and mechanically connected to saidobject, and anti-hunting means for substantially preventing oscillationof said object about the position of correspondence with said pilotdevice comprising a saturable core reactor having an alternating currentwinding connected to said receiving device and a direct current controlwiding energized in response to the motor current so that a voltagedependent upon motor current is supplied to said receiving device toeffect rotation thereof in a direction to reduce the motor current.

14. A follow-up control system for causing a driven object to move intopositional agreement with a pilot device comprising in combination, anelectric motor for driving said object, a Wheatstone bridge connected tosaid motor for controlling the supply of current to said motor, amovable member for controlling the balance of said bridge, meansresponsive to positional disagreement of said pilot device and drivenobject for actuating said movable member to unbalance said bridge tocause said motor to drive said object toward correspondence withsaiddevice comprising an electrical motion transmitting device connectedto said pilot device and an electricalmotion receiving device having arotor element and a rotatably mounted stator element, one of saidelements being mechanically connected to said object and the othermechanically connected to said member and each of said elements beingprovided with a winding, electrical connections between one of saidwindings and a corresponding winding of said transmitting device, andantihunting means comprising a saturable core reactor having analternating current winding connected to the other winding of saidreceiving device and a direct current control winding energized inresponse to the motor current for varying the voltage of said reactor sothat a currentis supplied to said other winding of said receiving deviceto produce rotation of said receiving device and said member in adirection to reduce the current to said motor.

15. A follow-up control system for moving a driven object intopositional agreement with a pilot device comprising in combinationdriving means for said object, means for controlling said driving means,means responsive to positional disagreement of said pilot device andobject and having mechanical connections to said control means foractuating said control means to cause said driving means to drive saidobject toward correspondence with said pilot device, a, flexible memberincluded in said connections and means responsive to an operatingcondition of said driving means for deflecting said flexible member soas to actuate said control means to reduce the torque of said drivingmeans thereby substantially to eliminate hunting.

16. A follow-up cor irol system for causing a driven'object to move intopositional agreement with a pilot device comprising an electric motorfor driving said object, means for controlling the.

17. A follow-up control system for causing a driven object to move intopositional agreement with a pilot device comprising an electric motorfor driving said object, a Whe'atstone bridge for controlling the supplyof current to said motor, a movable member for controlling the balanceof said bridge, means responsive to positional disagreement of saidpilot device and driven object for actuating said control means toenergize said motor to drive said object toward correspondence with saidpilot device comprising a mechanical differential device connected tosaid pilot device and driven object and having a mechanical connectionto said movable member, a flexible member included in said connections,and anti-hunting meansresponsive to the current supplied to said motorfor actuating saidmovable member in a direction to reduce the current tosaid motor comprising a saturable core reactor having an alternatingcurrent coil and direct current control winding connected to beresponsive to the current of said motor for varying the voltage of saidalternating current coil, and means responsive to said variation involtage for deflecting said flexible member.

18. A follow-up control system for driving an object into positionalagreement with a pilot device comprising in combination, driving meansfor said object, a Wheatstone bridge for controlling the energization ofsaid driving means, each of the arms of. said bridge being provided witha plurality of taps each having a spring contact, said contacts beingarranged in spaced apart relationship with respect to each other, amovable member for actuating said contacts into engagement with eachother thereby to short circuit portions of said bridge arms and toproduce progressively increasing unbalance of said bridge, meansresponsive to positional disagreement of said pilot device and drivenobject for actuating said member to unbalance said bridge and energizesaid driving means to drive said object toward correspondence with saidpilot device, and means for compensating the spring pressure of saidcontacts against said member.

19. A follow-up control system for driving a driven object intopositional agreement with a pilot device comprising in combination, anelect- 'tric motor for driving said object, a Wheatstone bridge forcontrolling the energization of said motor, each of the arms of saidbridge being provided with a plurality of taps each having a springcontact, said contacts being arranged in groups and in spaced apartrelationship with respect to each other, a member for actuating saidcontacts into engagement with each other to short circuit portions ofsaid bridge arms in succession to efl'ect progressively increasingunbalance of said bridge, means responsive to positional disagreement ofsaid pilot device and driven object for actuating said member to causesaid motor to drive said object toward correspondence with said pilotdevice, and means for compensating the spring pressure of said contactsagainst said member comprising a pair of continuously energizedelectromagnets spaced apa t from 'each other and an armature connectedto said member and arranged in the space between said magnets so thatthe force of attraction between said armature and one of said magnets isincreased as said armature approaches said one magnet.

KENNETH K. BOWMAN. GAROLD A. KANE.

